1. Field of the Invention
The invention relates to a process for the preparation of bitumen/polymer compositions with a reinforced multigrade nature. It further relates to the application of the compositions obtained to the production of bitumen/polymer binders for coatings and in particular for road surfacings or for watertight facings.
Bitumen/polymer compositions with a reinforced multigrade nature is understood to mean, according to the invention, bitumen/polymer compositions which exhibit a wide plasticity range. The said range is defined as the difference between the ring-and-ball softening temperature (abbreviated to RBT), which reveals the hot properties of the binder or bitumen/polymer composition, and the Fraass brittleness point, which reveals the cold properties of the bitumen/polymer composition. The bituminous binder consisting of/or based on the bitumen/polymer composition will become increasingly resistant to hot stresses and cold stresses as the plasticity range widens.
The ring-and-ball softening temperature (RBT) and Fraass brittleness point quantities mentioned above are determined from standardized procedures as indicated hereinbelow:
ring-and-ball softening temperature:
determined according to NF Standard T 66 008 and expressed in .degree.C.; PA2 Fraass brittleness point:
determined according to NF Standard T 66026 and expressed in .degree.C.
2. Background Art
A process for the preparation of bitumen/polymer compositions with a reinforced multigrade nature is described in French Patent Application No. 94 04577 of 18.04.1994 on behalf of the Applicant Company. This process comprises bringing a bitumen or mixture of bitumens into contact, the operation being carried out at temperatures of between 100.degree. C. and 230.degree. C. and with stirring for a period of time of at least 10 minutes, with, with respect to the weight of the bitumen or mixture of bitumens, 0.5% to 20% and preferably 0.7% to 15% of a sulphur-crosslinkable elastomer and a sulphur-donor coupling agent in an amount capable of providing an amount of free sulphur representing 0.1% to 20% and preferably 0.5% to 10% of the weight of the sulphur-crosslinkable elastomer in the reaction mixture formed from the ingredients bitumen or mixture of bitumens, elastomer and coupling agent, in order to produce a sulphur-crosslinked composition, and then incorporating in the reaction mixture resulting from the vulcanization with sulphur, which is maintained at a temperature between 100.degree. C. and 230.degree. C. and with stirring, 0.005% to 5% and preferably 0.1% to 2.5%, by weight of the bitumen, of an acidic adjuvant comprising at least one compound chosen from the group formed by phosphoric acids, boric acids, sulphuric acid, the anhydrides of the said acids and chlorosulphuric acid and in maintaining the reaction mixture containing the acidic adjuvant at a temperature of between 100.degree. C. and 230.degree. C. and with stirring for a period of time of at least 20 minutes. The acidic adjuvant which can be employed in the process of French Patent Application No. 94 04577 can comprise in particular one or a number of the compounds chosen from H.sub.3 PO.sub.4, P.sub.2 O.sub.5, H.sub.3 BO.sub.3, B.sub.2 O.sub.3, H.sub.2 SO.sub.4, SO.sub.3 and HSO.sub.3 Cl.